Study of colloidal phosphorus in barium phosphate glasses by gas chromatography and SAXS

Barium phosphate glasses were obtained by melting different precursors in oxidizing or reducing atmospheres. These glasses become orange-red after a heat treatment at 520 °C for 2 h. Glass samples were analyzed by X-ray diffraction, optical absorption spectroscopy, and SAXS. Hydrogen released by the decomposition of NH₄H₂PO₄ reduces the valence state of phosphorus ions to neutral, and colloidal dispersions formed during a post heat treatment are responsible for the glass coloration. The particle size-distribution function was determined by SAXS. The coloration effect is caused by the change of the particle size distribution. The maximum colloidal particle size is displaced from 75 to 250 Å after the heat treatment.